1.Technical Field of the Invention
The present invention relates to an illuminator and a projector using the illuminator.
2.Description of Related Art
An effort has been made to enhance the contrast of an image of a projector by controlling an emitting light volume of a metal halide lamp, i.e. a light source, in accordance with the average illuminance of the image (see Japanese Patent Laid-Open Publication No. Hei 5-66501).
Alternatively, instead of varying the emitting light volume of the light source, the light volume is adjusted by an optical lens stop to enhance the contrast of the image (see Japanese Patent Laid-Open Publication No. 2002-23106).
However, the majority of projectors nowadays use a high-pressure mercury lamp as the light source. When the emitting light volume of such a high-pressure mercury lamp is adjusted in the same manner as described in the Japanese Patent Laid-Open Publication No. Hei 5-66501, the 100% emitting light volume can be attenuated only to approximately 70% and, consequently, the contrast of the image cannot be sufficiently enhanced.
On the other hand, when the light from the light source is extremely attenuated using the optical lens stop shown in the Japanese Patent Laid-Open Publication No. 2002-23106, a heat is generated and concentrated on the optical lens stop, which can exert undesirable influence on the adjacent optical components or the like.
Further, when the optical lens stop is used to extremely attenuate the light from the light source to 30 to 40%, unevenness of illumination may become prominent on account of minute errors in disposition of the components such as a lamp, a light shield and an integrator, which may cause serious illumination unevenness by exchanging the lamp etc.